Clark's? Western? Or both? (Some elaboration)
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Just a smattering of responses. The consensus is that this bird is OK for Western, as the facial pattern in winter is nearly identical between the two species, with the differences coming down to bill color (most important) and the amount of white (thinner black neck stripe and more white on the body/flanks of Clark's).
Perhaps the initial photo was unclear. I still think this bird is a true intergrade or hybrid, as hopefully shown better on a second photo [below] (not quite as sharp as the first, but cropped a bit more tightly).
(You will need to expand the photo to full size to see these features more clearly)
Even if we accept that the facial patterns are indistinguishable in winter (which, for the record, I do not concede, both by my admittedly somewhat limited experience and as that "fact" is not supported by multiple references, rather most state that they can be "difficult to distinguish"), this second photo more clearly shows the extent of white along the flanks and mottling of the back (as well as showing what I would submit is a facial pattern much more consistent with Clark's, as the black clearly does not extend down to the eye and there is a definite black stripe from the eye to the base of the beak, a typical feature of Clark's), but with the greenish yellow beak of a Western.
So, that's my take anyway. Thanks to those who responded. Maybe a bit of an arcane - and perhaps pointless - effort, but I think it is worthwhile to fully observe and occasionally really look closely at some of our more common species.
There is a tremendous amount of variation in nature, both in appearances and behavior, and close observation (if it doesn't drive one crazy) can be very rewarding and sometimes reveal aspects that even the "experts" have not noted. Remember that we are all citizen scientists to greater or lesser degrees, and with so many more birders than expert ornithologists out in the field, one is quite likely to observe "new" findings. So, please take the time to observe and add comments and notes to your reports and eBird checklists - more data, more better!
To more discoveries,
On Wednesday, December 25, 2019, 10:34:05 AM PST, Richard Bradus <grizzledjay@...> wrote:
I've been seeing a lot of "Western type" Grebes lately that have me confused, mostly the typical wintertime variants with black that goes down to the eye (or gray that covers the eyes and upper cheek), in between what we consider true Clark's or Westerns. But this one (seen Dec. 17 in the waters off the eastern end of the Golden Gate Yacht Club Lagoon) is a bit more interesting:
(Photo can be enlarged if it does not display fully on your device)
It has the facial pattern of a Clark's (mostly) and a fair amount of white mottling on the back, yet the bill is that greenish yellow color characteristic of a Western. I've been told (and have also read in a couple of sources) that bill color (and shape to some extent) is the best determinant as to species, but this one looks like a true "intergrade" to me. I think it is a hybrid. So a call out to experts or other interested parties: any thoughts?
And to all a wonderful holiday.